A typical circuit board includes a section of circuit board material (e.g., fiberglass, copper, vias, etc.) and circuit board components which are mounted to the section of circuit board material. Examples of circuit board components include integrated circuits (ICs), resistors, and inductors. Typically, these circuit board components generate heat during operation. A fan assembly typically generates an air stream that passes over the components and carries heat away. The air stream removes the heat so that the components do not operate in an unsafe temperature range, i.e., an excessively high temperature range that would cause the components to operate improperly (e.g., generate a signal incorrectly) or sustain damage (e.g., overheat, burnout, etc.).
Some ICs include heatsinks to facilitate cooling. In general, a heatsink is a flanged metallic device that attaches directly to the package of the IC. As the IC generates heat, heat flows from the IC package to the heatsink, and dissipates into the surrounding air. The air stream generated by the fan assembly then carries the heat away thus cooling the IC.
Some electronic enclosures (e.g., computer housings, boxes, towers, cabinets, etc.) or structures neighboring a circuit board provide limited space in the vicinity of the circuit board components. For example, the side of the circuit board on which the components mount may be close to a neighboring structure such as the side of the enclosure, the side of a card cage, the side of a neighboring circuit board, etc. In such situations, the open space around the circuit board components may be too small to allow an air stream provided by the fan assembly to adequately cool the components with or without conventional heatsinks. For such situations, alternative cooling approaches can be used.
One alternative approach to removing heat from circuit board components when space around the components is limited is called the heatpipe approach. A heatpipe is a device that moves heat using a process known as xe2x80x9cvapor phasexe2x80x9d. A typical heatpipe includes an enclosed fluid pathway (e.g., a coil, a manifold, etc.). A portion of the fluid pathway is typically epoxied to the circuit board components. When the circuit board components (a heat source) heat up, fluid in that portion absorbs heat energy and changes from the liquid state to the gas state, i.e., the fluid boils. The vapor pressure forces the fluid (which is now the gas state) to a cooler portion of the pathway which is distal to the circuit board components. At this cooler portion, the fluid releases heat and condenses back into a liquid. That is, heat passes from the fluid into the cooler pathway walls and into the surrounding environment. The wicking action then sends the fluid (which is now back in the liquid state) back to the heat source portion of the pathway to absorb and carry away more heat in a cyclical manner.
Another alternative approach to removing heat from circuit board components when open space is limited is called the thermal transfer material approach. In this approach, thermal transfer material is placed between a circuit board component and a neighboring object such as the wall of an enclosure. The thermal transfer material conveys heat from the component to the neighboring object in order to dissipate the heat, via thermal conduction.
Yet another approach to removing heat from circuit board components when space around the components is limited is called the redesign approach. In this approach, the physical layout is modified (e.g., the enclosure is made larger, the circuit board components are moved away from neighboring structures, etc.) to permit a healthy air stream to adequately flow over the components and carry heat away.
Unfortunately, there are deficiencies to the above-described conventional approaches to cooling circuit board components when space in the vicinity of the circuit board components is limited. For example, in connection with the conventional heatpipe approach, heatpipe assemblies are typically very complex and require special handling in order to work properly (e.g., compared to heatsinks). Accordingly, heatpipes are prone to malfunction over time (e.g., a leak, etc.) due to their complexity. Additionally, when there is a problem (e.g., when the heatpipe fails, when a component epoxied to the heatpipe fails, etc.), the solution often involves removing the heatpipe from the components (e.g., ungluing the heatpipe from all components) which can cause other problems such as damage to a component that otherwise had functioned properly. Furthermore, the cost of heatpipe components (e.g., the tubing, the fluid, manufacturing costs, etc.) often makes the heatpipe approach prohibitively expensive. Also, depending on the board design and the geometry of the heatpipe, there could be adverse effects to electromagnetic interference (EMI) containment of the board since the heatpipe might act as an antenna.
Additionally, in the conventional thermal transfer material approach, the thermal transfer properties of the thermal transfer material are often affected by the pressure of the thermal transfer material on the circuit board components. That is, if the thermal transfer material is not pressed tightly enough between a circuit board component package and a neighboring structure (e.g., the wall of a card cage), the thermal transfer material will not convey heat properly from the component to the neighboring structure. Alternatively, if the thermal transfer material is pressed to tightly between the component and the neighboring structure, the mounting location of the component (e.g., the solder joints) can sustain damage causing the component to operate improperly. Unfortunately, the physical tolerances which dictate the distance between component and the neighboring structure may vary significantly and thus make this approach ineffective and problematic with some implementations not conveying enough heat due to too little pressure on the thermal transfer material, and some implementations damaging the component mounting locations due to too much pressure.
Furthermore, in the conventional redesign approach, the physical layout must be altered (e.g., increasing the size of an enclosure, providing more distance between a circuit board and a neighboring structure, etc.) to allow a healthy air stream to flow over the circuit board components. Such an approach is not always a practical option. In some situations, a particular application may require a small enclosure or close neighboring structures. For example, some computer equipment configurations may include circuit boards which are mounted to metal plates for EMI isolation (e.g., line card assemblies for a data communications device). Increasing the distance between the circuit boards and the metal plates on which they are mounted for each circuit board may be impractical due to size constraints. As another example, a mature design may call for an improvement by replacing one chipset with a higher-power, hotter-running chipset in order to obtain a cost/performance advantage over a competitor. In such a situation, the requirement of a redesign of the entire physical layout may be prohibitively expensive. Accordingly, there may be situations in which the redesign approach is impractical or unavailable.
In contrast to the above-described conventional approaches to cooling circuit board components, the present invention is directed to techniques for cooling a circuit board component mounted to a circuit board which uses a heatsink having a receptacle that fastens to a support assembly that supports the circuit board, and an adjustable member that engages the receptacle and is movable relative to the receptacle in order to control a distance between the adjustable member and the component. The heatsink can thus be moved to a position (e.g., in full contact with a circuit board component package, into contact with thermal transfer material that contacts the circuit board component package, etc.) which enables the heatsink to convey heat from the component to another structure such as the support assembly thus cooling the component during operation even if the component resides in a location where space is limited.
One arrangement is directed to a circuit board assembly which has (i) a circuit board including a section of circuit board material and a circuit board component mounted to the section of circuit board material, (ii) a support assembly that supports the circuit board, and (iii) a heatsink that cools the circuit board component mounted to the circuit board. The heatsink includes a receptacle that fastens to the support assembly, and an adjustable member that engages with the receptacle. The adjustable member is movable relative to the receptacle in order to control a distance between the adjustable member and the circuit board component. Accordingly, the adjustable member can be positioned properly (e.g., with the correct pressure) for proper heat transfer therethrough. Moreover, the circuit board assembly can include multiple heatsinks for cooling multiple circuit board components with the adjustable member of each heatsink being individually adjusted in a customized manner to accommodate any tolerance differences in the distances between the support assembly and the circuit board components.
In one arrangement, the receptacle of the heatsink defines an internally threaded surface. In this arrangement, the adjustable member defines an externally threaded surface such that the adjustable member threads within the receptacle and such that a distance between the adjustable member and the circuit board component varies as the adjustable member threads within the receptacle. Accordingly, the distance between the adjustable member and the circuit board component can be changed simply by threading the adjustable member within the receptacle (e.g., turning the adjustable member using a torque wrench).
In one arrangement, the receptacle includes a collar that defines the internally threaded surface of the receptacle, and an externally threaded surface. In this arrangement, the receptacle further includes a retaining nut that defines an internally threaded surface that corresponds to the externally threaded surface defined by the collar such that the retaining nut threads around the collar. Accordingly, the receptacle can be securely attached to the support assembly.
In one arrangement, the circuit board assembly further includes thermal transfer material disposed between the adjustable member and the circuit board or component. The thermal transfer material facilitates heat transfer between the circuit board or component (e.g., the top surface of the component) and the adjustable member (e.g., the top surface of the adjustable member).
In one arrangement, the circuit board assembly further includes an adhesive that holds the thermal transfer material to the adjustable member. The adhesive prevents the thermal transfer material from separating from the adjustable member prior to adjusting the adjustable member so that the thermal transfer material is held in place by friction between the component and the adjustable member.
In one arrangement, the thermal transfer material includes a first layer of phase-change material that contacts the adjustable member, a second layer of phase change material that contacts the circuit board component, and foil disposed between the first layer of phase-change material and the second layer of phase-change material. The foil improves the thermal transfer properties of the thermal transfer material.
In one arrangement, the adjustable member further defines a cavity to receive a torque wrench attachment. This enables a user to install the adjustable member in a consistent and easily repeatable manner.
In one arrangement, the adjustable member includes a metallic element. In this arrangement, the support assembly includes a section of sheet metal, and a set of standoffs that connect the section of sheet metal to the circuit board. In this arrangement, the metallic element and the section of sheet metal preferably form an EMI shield. Accordingly, circuitry within the circuit board component (as well as other circuitry on the circuit board) is protected against EMI which could otherwise cause improper operation.
The features of the invention, as described above, may be employed in electronic equipment and methods such as those of Cisco Systems of San Jose, Calif.